PON evolution and future FTTH market prediction: NG-PON2

Contributors: José Salgado, Rong Zhao, Nuno Monteiro, and Pauline Rigby

NG-PON2

TWDM-PON Key features:
Build on XG-PON1
40 Gbps UP TO 80 gBPS (total throughput)
Coexistance with GPON networks

  The next-generation technology, NG-PON2, is expected to increase PON capacity to at least 40 Gbps downstream and at least 10 Gbps upstream by 2015. Since the implementation is further ahead in time, it opens up the possibility of using more innovative approaches. Some of the proposals under consideration by FSAN include:

  • 40Gbps TDM PON
  • Time- and wavelength-division multiplexed (TWDM) PON
  • WDM-PON
  • Coherent ultra-dense WDM-PON (PON UDWDM)
  • Orthogonal Frequency Division Multiplexing (OFDM) PON
TWDM-PON Challenges:
Tunable receivers and ransmitters at ONU
Spectrum allocation

  FSAN has already selected TWDM-PON as the primary approach for NG-PON2, which is now in the process of being standardized by ITU-T. Operators consider TWDM-PON to be less risky, less disruptive and less expensive than other approaches because it reuses existing components and technologies. TWDM-PON can be viewed as multiple XG-PON1 systems operating on different pairs of wavelengths, so that they can be “stacked” onto the same physical fibre plant.

NG-PON2 architecture

NG-PON2 architecture

  NG-PON-2 was also designed to “pay as you grow”, allowing operators to place the different technologies – GPON, XG-PON and NG-PON2 – on the same optical distribution network. Coexistence is ensured by a passive element, called the coexistence element (CE), which combines/splits the various wavelengths associated with each technology generation.

  The main challenges of implementing NG-PON2 are the spectrum allocation (bearing in mind that compatibility with sensitive RF services is a must) and the need for “colourless” ONTs, which must be able to send and receive signals on any of the specified wavelengths. The ONT transmitter must be tunable while the receiver requires a tunable filter.

Coexistence element (draft ITU-U G.989)

Coexistence element (draft ITU-U G.989)

  Colourless ONTs based on tunable transmitters and receivers are likely to be more expensive than GPON ONTs. Optical component vendors are developing new technologies to help bring down costs. The use of photonic integrated circuits (PICs) in the ONT is highly attractive because a low-cost manufacturing process would enable mass deployment.
  Furthermore, since tuning technologies mainly rely on temperature control, a key challenge is to maintain low power consumption in the ONT in compliance with the stringent EU Code of Conduct on Energy Consumption of Broadband Equipment. Ingenious power saving mechanisms will help to reduce the power consumption.

  Four variants of TWDM-PON are currently being developed by ITU-T Study Group 15:

  • Basic: 40 Gbps downstream and 10 Gbps upstream capacity, using four wavelengths
  • Extended: 80 Gbps downstream and 20 Gbps upstream capacity, using eight wavelengths
  • Business: Symmetrical services, 40/40 Gbps and 80/80 Gbps
  • Mobile fronthaul: point-to-point WDM overlay

  It is also expected that NG-PON2 devices will support mobile backhaul timing specifications (such as IEEE 1588v2 Boundary Clock and Transparent Clock) to support the precise frequency and phase time requirements in mobile networks.

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